1. Technical Field
The present invention relates to a data transmission and reception system in which a master device and slave devices perform two-way data communications with each other. The invention also relates to a master device and a slave device (semiconductor integrated circuits) used in such a data transmission and reception system.
2. Related Art
For example, in a system including a central control unit and a terminal processing apparatus, the central control unit and terminal processing apparatus perform data transmission and reception with each other so as to transmit data storing such as the state of the terminal processing apparatus. In particular, in a system including multiple terminal processing apparatuses, a central control unit and each terminal processing apparatus must perform transmission and reception of data indicating the state of the terminal processing apparatus with each other. For this reason, the data transmission and reception system is configured so that the central control unit is provided with a master device and each terminal processing apparatus is provided with a slave device.
Two-way communications are effective in reducing the number of signal terminals or wire lines in such a data transmission and reception system. For example, use of three types of signals, that is, data, a clock signal, and a reset signal, allows two-way communications. Specifically, after a system is reset by activating a reset signal temporarily, a master device starts to transmit data and a clock signal to a terminal slave device. Subsequently, the master device completes the transmission in synchronization with a rising edge of an n-th (n is predetermined natural number) pulse in the clock signal. At the same time, the terminal slave device starts transmission to the master device.
However, if such a communication method is applied to a system having a configuration in which a relay slave device (also referred to as a “bridge chip”) having a particular function different from that of a terminal slave device is coupled in series between a master device and the terminal slave device and the same three types of signals are used, there occurs a conflict such as one where the two slave devices simultaneously transmit transmission signals due to a difference between timings at which the two slave devices switch between transmission and reception. Such a conflict may have a negative effect, such as shortening of life, on the devices. On the other hand, if a control signal for controlling the switching of the communication direction is used, the number of signal terminals or wiring lines is increased. This is not preferable in terms of the product specification.
As a related-art example, JP-A-05-2538 (pp. 1 to 2, FIG. 1) discloses a parallel data communication method for preventing an increase in the number of control lines caused by an increase in the number of functions. In this parallel data communication method, a signal line includes multiple control lines for transmitting status information for providing notification of the operating state of an apparatus to the other devices or command information for specifying the operating state of an apparatus from another apparatus. Some of the control lines transmit a switching signal for switching the meaning of status information or command information transmitted through a data line or a remaining control line. As is understood from the above description, JP-A-05-2538 uses the multiple control signals and therefore the problem of the increase in the number of signal terminals or wiring lines is not solved.